The elderly tend to be afflicted with impairments of several cognitive processes, including a decreased ability to pay attention, perform multiple tasks, and to time short intervals. Some models suggest a close interaction of timing and attention. The proposed studies hypothesize that attention and timing involve similar brain regions, in particular motor areas in the frontal lobe. In addition, it is predicted that dysfunction of the frontal motor areas is responsible for the age-related impairments in attention and timing. This dysfunction is due, in part, to the loss of cholinergic neurons of the nucleus basalis magnocellularis (NBM). The proposed studies do the following: 1) examine the effects of damage to motor cortex and NBM projections to motor cortex on attention and time estimation, 2) compare age-related changes of attention and timing in rats and humans, 3) examine the relationship between age-related loss of NBM neurons and impairments in attention and timing, and 4) investigate the effects of aging and brain damage on attention-related neuronal activity in motor cortex. The proposed behavioral studies with rats and humans involve similar versions of a simultaneous temporal processing (STP) task. In the STP task, subjects' learn to associate auditory and visual cues with short and long fixed time intervals, and are then tested on their ability to produce/estimate this time interval under different attentional demands. In a focused attention condition, only one cue is presented to subjects. In a divided attention condition, both cues are presented and must be attended to in order to respond correctly. The focused attention condition serves as a baseline measure of performance. The central empirical question concerns how aging and lesions (in rats) affect timing performance in divided attention conditions, relative to focused attention conditions. Model fits using scalar-expectance theory facilitate comparison between the human and rat behavioral data and potentially provide a functinoal interpretation of the effects of aging and lesions on focused and divided attention. Overall, the studies in this proposal will enhance our knowledge of the brain systems participating in attention and timing. Importantly, new information will be revealed that will elucidate the neural mechanisms responsible for age-related impairments in attention and timing. This new knowledge will provide directions for the development of treatments.